Flexible dielectric film with high energy density based on chitin/boron nitride nanosheets

•Chitin was investigated for the first time as dielectric film capacitors.•Chitin/BNNS composites were fabricated through dissolution/regeneration process.•The dielectric properties of composites were improved by the incorporation of BNNS.•The composites also showed enhanced mechanical properties and thermal stability. Polymer-based film capacitors have attracted considerable attention owing to their important applications in both electronics and electrical systems. However, ever-growing environmental challenges stimulate a great demand for exploring renewable dielectric materials. Herein, flexible film dielectrics based on regenerated chitin and boron nitride nanosheets (BNNSs) were fabricated, for the first time, through a straightforward low-temperature dissolution/regeneration process, in which a “green” KOH/urea aqueous system was chosen as both the solvent of chitin and the exfoliation agent of BNNSs. Benefit from the excellent intrinsic properties of embedded BNNS, substantially elevated dielectric performances were achieved, including much suppressed dielectric loss along with significantly enhanced breakdown strength. Particularly, an ultrahigh charge-discharge efficiency of above 90% could be well-maintained in composites with only 6 wt% BN loading, even the applied electric field up to 400 MV m−1, therefore resulting in a marvelous discharge energy density of 8.67 J cm−3. Furthermore, aside targeted excellent dielectric properties, the resultant composites also possessed improved mechanical and thermal properties. This strategy developed here not only broadens the application of chitin, but also opens a new window for the establishment of next-generation environment-friendly dielectrics with superb dielectric properties.